First of all, I recommend reading “Chariots of the Gods” by Erich Von Dannikin.
Von Dannikin, who was several bricks shy of a load, wrote this book to prove Earth was populated by “ancient astronauts.” I advise reading this silly book to study the techniques he used – because many fundamentalists use exactly the same techniques.
In one example, he takes a photo of a Mayan Stele, a stone with many carvings on it. One carving shows a crouching warrior in full regalia. Von Dannikin crops this photo to show only the warrior, then turns it 90 degrees, so the warrior appears to be looking up. He prints it next to a picture of an astronaut in a space capsule, and says the Mayans were showing us a carving of an ancient astronaut!
Now note the techniques:
- He picks and chooses his evidence. The earth was populated long before the Mayans appeared (after the time of Christ.) How a Mayan would know more than, say a Greek or Roman is not explained – but they had the right carving.
- He manipulates the evidence – the warrior is shown crouching, not reclining for takeoff. But he turns the photograph to make it look that way.
- He dramatically restricts your access to information. The photo is cropped so you can’t see what else is on the stele. He doesn’t tell you we know all about this warrior – the Mayans could write and we can read their writing.
- He tries to overwhelm you – there are many examples like this in the book, and he keeps piling them on, so you don’t have time to refute each and every one in detail.
- He tries to shift the burden of proof, demanding you explain the things he presents if you think he’s wrong (but see point 3 and 4 above.)
To deal with these techniques, first select one point or claim and investigate it thoroughly. If a Bible verse is offered as proof, go and read not only that verse, but the whole book . Do not allow them to overwhelm you – stick on the one point until you settle it, then move onto the next. In a short time you will be able to say, “You were dead wrong on the first three points, so why should I continue this charade?”
Remember, the burden of proof is on the one advancing the claim – they have to prove their point, you don’t have to disprove it.
Now in this particular case, the pastor you say rejects the eucharist. Have him prove Jesus was wrong when He instituted the eucharist. If he can’t do that, the rest of his argument is not worth considering.
If a church - any church - does or says or believes or uses something that can be seen as a thing that is condemned in the Bible, that’s often enough to prove that the church in question is “pagan”.